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The Sky This Week, 2016 February 9 - 16

A secret in a sword.
Messier 42, the "Great Orion Nebula" and surroundings
Imaged from near Morattico, VA, 2014 January 1
80 mm (3.1-inch) f/6 refractor and Canon EOS Rebel T2i DSLR

The Moon returns to the evening sky this week, waxing through her crescent phases as she moves through the faint autumnal constellations. First Quarter occurs on the 15th at 2:46 am Eastern Standard Time. Luna treads a lonely path through the sky, passing no bright objects until the evening of the 15th, when she closes in on the bright star Aldebaran in the constellation of Taurus, the Bull. Residents in the Pacific Northwest will see Aldebaran slip behind the Moon’s dark limb shortly before moonset that night.

We are now at that time of the year when the days are becoming noticeably longer. The total length of daylight is now well over an hour more than it was at the winter solstice, and the rate at which daylight is being added amounts to nearly three minutes per day. Nevertheless, you still have plenty of darkness to enjoy the bright stars of the winter constellations. The Great Winter Circle, dominated by the prominent constellation of Orion, the Hunter, straddles the meridian at 8:30 pm. This area of the sky plays host to one of the most remarkable sights that you’ll find in all of Nature, the Great Orion Nebula. To find it, locate the three prominent "Belt Stars" that are Orion’s most striking feature. Hanging below the left-most star of the belt you’ll see a small line of three fainter stars known as "The Sword". From a dark location the middle one of these will look a little fuzzy to the naked eye. Point a pair of binoculars at the sword and you’ll see that the middle star is surrounded by a soft amorphous glow. Viewing through telescopes of increasing aperture reveals the star in the center of this nebulosity to be a quadruple star system known as the Trapezium, surrounded by convoluted swirls of softly glowing gas. Bright streaks are silhouetted behind dark clumps of material, rendering the entire nebula as a great three-dimensional structure that defies verbal description as well as the artist’s ability to render it. In large telescopes the central region glows with a ghostly greenish tint. What you are looking at is the center of a vast cloud of interstellar gas and dust, the core of a huge cloud of material that is the site of rampant new star formation. The stars of the Trapezium are very energetic young stars that emit copious quantities of ultraviolet light, causing the surrounding gas to fluoresce with characteristic colors of hydrogen and doubly-ionized oxygen. If our eyes were sensitive to the spectral lines of these atoms the entire constellation would be shot through with the glow of these vast clouds of material that contain enough stuff to form over 10,000 stars as massive as our Sun. Most of Orion’s bright stars formed from this bright stellar nursery within the past few million years, and more will follow over the next few million. There are several other examples of these star-forming regions throughout the Milky Way Galaxy, but the Orion Nebula is one of the closest to us, about 1500 light-years distant, and is probably the largest in the Galaxy. Take advantage of its prominent placement to explore it on the next clear evening.

After studying the Orion Nebula for a while you can turn your attention eastward to focus on the rising planet Jupiter. Old Jove rises at around 8:00 pm and should be sufficiently high by 10:00 pm for a quick telescopic peek. If you’re up until midnight his placement becomes even better as he rises above the turbulence of the horizon. Point a small telescope at Jupiter on any night and you’ll see some sort of configuration of his four bright moons, but if you do so on the night of the 13th you’ll see a nice, symmetrical formation with two moons on either side of the planet. On the following night the planet’s famous Great Red Spot rotates onto the disc and is well-placed for viewing in a modest-aperture telescope.

Ruddy Mars is still a morning object, best observed before sunrise at around 6:00 am. At this time he’s on the meridian in the southern sky, glowing with his characteristic pinkish hue. He is beginning to brighten as we move closer to opposition in late May. His disc should start to show detail in telescopes of six-inches of aperture, and it will double in size by the time opposition occurs.

Saturn shines prominently near the bright star Antares in Scorpius. There’s a very nice color contrast between the two objects, and they are both bright enough to follow into morning twilight. A small telescope will provide a very rewarding view of Saturn, which will reach his opposition in early June.

Venus now rises after the onset of morning twilight, but you should still be able to find her low in the southeast well before the Sun breaks the horizon. Venus will linger in this position for the next few months before emerging into the evening sky later this summer.

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